The Wisconsin Constitution ties the size of the State Senate to that of the Assembly, by limiting its size to no less than 1/4, nor more than 1/3, of the size of the Assembly. Currently, Wisconsin is divided into 33 Senate Districts (1/3 of the current Assembly membership of 99) apportioned throughout the state based on population as determined by the decennial census, for a total of 33 senators. A Senate district is formed by combining three Assembly districts. Similar to the U.S. Senate, in addition to its duty of reviewing and voting on all legislation passed through the legislature, the State Senate has the exclusive responsibility of confirming certain gubernatorial appointments, particularly cabinet secretaries (as part of the system of checks and balances) and members of boards and commissions. Senators are elected for four-year terms, staggered so that approximately half of the Senate is up for election every two years. If a vacancy occurs in a Senate seat between elections, it may be filled only by a special election. The Senate chamber is in the south wing of the Wisconsin State Capitol, in Madison.

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Senators elected or re-elected in the fall of 2008 will receive an annual salary of $49,943. In addition to their salaries, senators outside Dane County may receive a per diem up to $88 to cover living expenses while they are in Dane County on state business. Members of the Madison delegation may receive a per diem up to $44 to cover expenses. Each senator also receives $75 per month in "out-of-session" pay when the Legislature is in session for three days or less. Over two years, each senator is allotted $66,008 to cover general office expenses, printing, postage and district mailings.[citation needed]

Following the 2016 elections, The Wisconsin State Senate maintained a Republican majority in January 2017 for several reasons. Democrat Julie Lassa lost her re-election to Patrick Testin. Following the retirement and death of Republican Senator Rick Gudex, Republican Dan Feyen defeated Democrat Mark Harris. The Senate has 20 Republicans and 13 Democrats.